Coelomocytes are the immune effectors of the sea urchin and have shown to respond to environmental and experimental challenge by the activation of stress markers. We extended our in vivo studies to in vitro short term cultures of sea urchin coelomocytes by analysing their response to temperature being stress, acid pH and heavy metals, using the hsp70 protein as a stress marker. We found that the in vitro time course of temperature stress recapitulates results obtained in vivo where the highest overexpression was observed after 1 hour. Coelomocytes overexpress hsp70 in a time-dependent manner when cultured for 1 to 6 hr at pH 4.7 +/- 0.2 in isotonic buffer, supplemented with EDTA as anticoagulant. A peak in the level of hsp70 expression was observed at 2 hr of culture, corresponding to a 10-fold increase over the levels of control coelomocytes cultured at pH 7.3 +/- 0.2. The effect of different concentrations of CdCl2 in the culture over a period of 4 hr was also tested. We found that CdCl2 greatly increases the hsp70 expression, with 10(-3) M the dose at which the highest overexpression is observed.